I think Ezio dies of a heart attack. I recall one of the developers stated that he was a reflection of Ezio at that age. The Templar logo (if it's actually there) could be a metaphor not that he is a Tenplar. I've heard another theory quite interesting saying that he's Federico (Ezio's brother) but I strongly disagree with that theory, but I just though it was quite interesting. But that would mean that Ezio saw his self and knew he had done his part, that is why he looks at his daughter and wife with a somewhat smile. Besides, WE ALL KNOW HE HAS EAGLE SENSE. He could have easily anticipated that.